Crystal Ho, from Macau, told a local newspaper on Tuesday that her picture had been circulated, mistakenly identifying her as the attacker.
The five-minute clip of the original assault went viral after user antonas1102 uploaded it to YouTube last Friday. As of yesterday, the video - which shows a woman smacking a kneeling man in the face at least 14 times - had gained more than one million views.
The picture shows Ho on the MTR. It was posted on Facebook by user Chloe Chan and shared by many, who believed she was the slapping woman. She was wearing black-framed glasses and had dyed blonde hair, similar to the accused, when the picture was taken.
The 18-year-old said she had contacted police in Macau, and hoped people would stop sharing her picture online.
A spokesman from the Office of the Privacy Commissioner for Personal Data said: "Cyberspace is boundless. The acts of publishing, reproducing and accessing the personal data of targeted individuals in an unfavourable light can be a far-reaching issue."
The privacy-defending bureau urged individuals to obtain consent from the subject of the material first before posting anything online.
Hong Kong police received a report at around 5.10pm on the day the video was posted. Police officers went to 38 San Ma Tau street in Kowloon City, where they arrested a 20-year-old female, surnamed Cheng, on suspicion of common assault.